Video Signal Amplifier

General Description

Video cassette recorders are becoming ever so popular and as it was to be expected the market is flooding with accessories that make the use of the VCR easier and enhance its operation. The circuit that we offer to you here is a broad band amplifier which will take the video signals from your VCR and will amplify them sufficiently to drive up to 3 monitors, TV sets (provided that they can accept direct video signals), or other VCR�s for recording from one video to up to three others. It will also make possible to record from one video to two others and at the same time have a monitor connected to check what you are recording. The

READ MORE

Wireless Audio-Video Transmission

This circuit provides you with wireless audio and visual transmission to a TV. The TV acts as a receiver, eliminating the need to buy a separate monitor. You can also hook it up to a VCR or CCD Camera, and even set up a remote CCTV security system!

fig: Block Diagram

Circuit Analysis:

Q3, VC1, C13, C16 and L3 all make up a colpitts oscillator circuit that fluctuates form 220~250MHz. You can regulate the frequency to any value within this threshold by tuning VC1 or L3. C13 modulates the signal rate. When the capacitance increases, so does the modulation. R9 and C16 bias the local oscillation. If you lower R9's frequency to 680W the oscillator's output

READ MORE

4 Watt FM Transmitter

General Description

This is a small but quite powerful FM transmitter having three RF stages incorporating an audio preamplifier for better modulation. t has an output power of 4 Watts and works off 12-18 VDC which makes it easily portable. It is the ideal project for the beginner who wishes to get started in the fascinating world of FM broadcasting and wants a good basic circuit to experiment with.

Technical Specifications - Characteristics

Modulation type: ........ FMFrequency range: .... 88-108 MHzWorking voltage: ..... 12-18 VDCMaximum current: ....... 450 mAOutput power: ............ 4 W

How it Works

As it has already been mentioned the transmitted signal is Frequency Modulated (FM) which means that the carrier�s amplitude stays constant and its frequency

READ MORE

Clap Switch

The circuit shown here for clap operated switch is inexpensive and easy to assemble by hobbyists of any level. Clap sound signals picked up by condenser microphone are first amplified by transistor T1, which is a simple common-emitter amplifier. Amplified signals are rectified by diode D1. Positive half cycle of clap signal is applied to a 3-stage DC amplifier formed by transistors T2, T3 and T4. Output from transistor T4 is used as a clock for flip-flop IC1 (7472). For each clap, the output of IC 7472 toggles alternately to on/off state.

Transistor T5 functions as relay driver since output level of IC1 is insufficient to drive a relay directly. The entire circuit, except the relay driver,

READ MORE

VGA to TV Converter

Here is the circuit for VGA to scart connection. It is basically a circuit which takes VGA signals and converts it to RGB + composite sync signal which can be fed to TV via SCART connector. VGA card picture components RED, GREEN and BLUE are already at the correct voltage level (0.7Vpp) and has correct impedance (75 ohm) for direct connection to correspondign inputs in the TV. What needs to be done is to combine separate horizonal and vertical sync signal from VGA card to one composite sync signal which is feed to TV video in pin in SCART connector. This sync signal conversion is done by the electronics in the circuit. The circuit has also sends correct level

READ MORE

4 Channel Tranceiver

This is a very simple RF transmitter circuit that consists of the Holtek HT-12E encoder chip and AM 418MHZ-transmitter module (WZ-X01). Using the hybrid RF xmit/receive modules make building the RF remote control a lot easy.

The transmitter can be powered with any voltage from +3 to +12V. The total current consumption is less than 5ma. Depending on the supply voltage, you may need to select a difference resistance value for the oscillator resistor R1. The recommended oscillator is Foscd (decoder) = 50 Fosce (encoder). See data sheet for more details.

The individual security code of the transmitter is preset by dip-switches S5, up to 256 combinations.

When any of S1-S4 is pressed the /TE pin is pulled low, and

READ MORE

Music to Light Modulator

A music-to-light modulator is a circuit which controls the intensity of one or more lights in response to an audio input. The problem in older circuits is that there was a direct electrical connection between the lights using mains voltages (110 to 250V AC) and the amplifier circuit low 9to 12 voltage levels. Any fault in the high voltage circuit could completely destroy the low voltage section (and give a nasty shock to anyone holding it.)

This potential problem has been overcome using the optocoupler. There is no electrical link between the two parts of the circuit. This kit introduces the opto-triac(3021) which is a further development of the optocoupler.An audio input controls a LED. The light from the

READ MORE